I have a msi x 58 pro mother board I replaced the power supply than the computer only gives off an amber light and no post
Did you reconnect the 4/8pin CPU power connector in the top left? Did you reconnect any power cables for graphics cards? Was the power supply the only thing you disconnected?
Sounds like EPs cable problem as above, but why was the PSU replaced? If the old one died, might have killed something else in the process.